Conman Mark Acklom is challenging a bid to seize his assets, five years after he was jailed for a notorious romance scam.
His lawyer told a judge that another man had admitted "pilfering" money from the victim, so it was difficult to know how much Acklom got.
Acklom, 50, was jailed for defrauding divorcee Carolyn Woods of £300,000 after wooing her and promising to marry her in Gloucestershire.
He used a false name and convinced her he was a wealthy banker and MI6 agent, before going on the run.
After being extradited from Switzerland in 2019, he admitted five charges, but had originally faced 20 charges that amounted to the theft of £750,000.
The Crown Prosecution Service now wants a court to establish exactly how much Acklom benefited from his crimes against Ms Woods - and what he has left - so it can try to confiscate his assets.
Prosecutors believe Acklom, who was first jailed for fraud when he was 18, has profited by £1.3m in his whole criminal career, in which he has been jailed in several countries.
His lawyer Martin Sharpe said prosecutors had abused the current confiscation process under the Proceeds of Crime Act (POCA) by not disclosing certain documents to the defence.
Mr Sharpe told a court in Bristol: "Paul Kaur is somebody who made admissions in interview [with police] that he had pilfered money from the complainant [Ms Woods].
"Part of the prosecution case was that the money Mr Acklom took from the complainant he channelled into Paul Kaur's account."
Mr Sharpe said: "In order to assess the benefit to Mr Acklom we need to find out how much money he [Kaur] took."
The lawyer said he didn't know how much money Mr Kaur took because he hadn't spoken to him and "because he wouldn't co-operate". He said he did not know how to contact Mr Kaur.
Mr Kaur, a businessman, told Sky News last year that he had worked for Acklom and, like Ms Woods, had been duped by him. He was never charged by police.
The bid to establish Acklom's benefit from the scam on Ms Woods began, effectively, from the day he was jailed and there have been several court hearings.
The latest is being held in front of Judge Martin Picton, who sentenced Acklom and told him at the time that he had acted in a "ruthless and utterly selfish manner".
The court was told Acklom had been freed from a Spanish jail last year, after being extradited at the end of his UK sentence, and was subject to a Spanish confiscation order of €374,000 euros (£321,000). His lawyer didn't know whether he had paid it.
Acklom was not in court in Bristol, and is living in Spain with his family and likely to become a Spanish citizen. His wife is Spanish.
Judge Picton said the hearings have "gone on for a bit now, to put it mildly", and said that, so far, he has not "heard a word from Mr Acklom".
He added: "It leaves me utterly bemused that we spend a lot of time, here today, tomorrow and another four days later establishing a [monetary] figure that has beyond even an outside chance of ever being recovered from a person living outside the jurisdiction."
Acklom's lawyer described the law around confiscation as "a confused landscape".
The hearing was adjourned for the day after the judge suggested lawyers from the two sides could discuss a possible agreement before coming back to court on Tuesday.
Judge Picton is expected to make a final decision on a confiscation order in April.
Paul Kaur has been asked for a response.
Ms Woods has always believed there was little chance of getting her money back from Acklom and has urged Barclays Bank to compensate her.
Acklom persuaded Ms Woods to put her money into a Barclays account and conned her into "lending" him regular amounts, up to £30,000 a day, through the bank which she says failed in its duty of care to question the payments.
A Barclays employee, a woman, was arrested and questioned by police early on in the investigation, but was never charged.
Barclays has been considering Ms Woods' claim for compensation since July and has promised her an update on its internal investigation this week.